docs: def _lock_renewer(lockref, interval, stop):
          """
          Renew the lock key in redis every `interval` seconds for as long
          as `self._lock_renewal_thread.should_exit` is False.
          """
          log = getLogger("%s.lock_refresher" % __name__)
          while not stop.wait(timeout=interval):
              log.debug("Refreshing lock")
              lock = lockref()
              if lock is None:
                  log.debug("The lock no longer exists, "
                            "stopping lock refreshing")
                  break
              lock.extend(expire=lock._expire)
              del lock
          log.debug("Exit requested, stopping lock refreshing")